I've pushed some work-in-progress to a git repository here:
https://git.lysator.liu.se/wiml/nettle
There's more to be done, but I would appreciate any comments or feedback
people might have. This is all the time I have available to put into it
right now, but I hope to return to it before too long.
The changes add two new public functions:
- ecc_point_set_compact() which is like ecc_point_set but accepts a
point in compact form (X and Y's parity/sign rather than X and Y)
- ecc_point_set_from_octets() which interprets a point converted to an
octet string by the rules set out in X9.62 and SEC.1, including compressed,
uncompressed, and hybrid points
I'm not terribly happy with the name ecc_point_set_compact(); does anyone
have a suggestion for a better name?
Internals:
Decompression works for P-256, P-384, and P-521, but it still needs sqrt
implementations for P-192 and P-224. P-224 will be much more complex than
the others (the c^((p-3)/4) shortcut doesn't apply), but there's a paper by
djb on computing square roots in it.
I added a second slot to the `ecc_modulo` struct to contain a sqrt(u)
implementation (as opposed to the existing sqrt(u/v) implementation). The
slot, and the typedef that describes functions in that slot, need better
names.
--
Wim Lewis / [email protected]
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